The invention relates generally to an installation for changing the temperature of fluid media. Of particular interest to the invention is an installation for the cooling of liquid media and the condensation of vaporous media by means of gaseous substances, especially air.
Installations having a gas-liquid contacting section and an indirect heat-exchange section are known. In the gas-liquid contacting section, a liquid to be cooled flows downwardly through a spray device and is collected in a vessel located at the bottom of this section. A stream of air flows through the gas-liquid contacting device countercurrent to the liquid and cools the latter. The air stream is thereby heated and also entrains some of the liquid, e.g. moisture. By virtue of the direct contact which occurs between the air and the liquid in the gas-liquid contacting section, the latter may be referred to as a wet-cooling section and the cooling operation itself may be referred to as wet-cooling.
The indirect heat-exchange section is composed of heat-exchange pipes which, if necessary, are provided with ribs or fins, and the medium to be cooled flows through the pipes. A stream of cooling air flows through the indirect heat-exchange section independently of the air stream flowing through the wet-cooling section. The air stream flowing through the indirect heat-exchange section cools the medium in the pipes and is thereby heated. Since contact between the air and the medium to be cooled is avoided in the indirect heat-exchange section, this may be referred to as a dry-cooling section and the cooling operation itself may be referred to as dry-cooling.
The heated air streams are mixed with one another above the cooling sections by means of a ventilator. Thereafter, they flow into the atmosphere together.
One of the purposes of installations having combined wet-cooling and dry-cooling systems is to avoid the vapor mists which are formed when wet-cooling is used exclusively and which are a result of the enrichment or saturation of the heated air with liquid. In this manner, the atmospheric pollution associated with such vapor mists may be prevented. Installations of this type also have the advantage that water losses due to evaporation may be reduced and, consequently, that the quantity of water required to make up for such losses may be reduced.
The wet-cooling section in installations of the type under discussion generally includes a number of inlet pipes having downwardly directed openings. The liquid to be cooled flows out of these openings into the spray device countercurrent to the upwardly flowing cooling air and then drips into the collecting vessel provided at the bottom of the wet-cooling section. On the other hand, the dry-cooling section mostly consists of finned heat-exchange pipes through which the medium to be cooled, which may be a gas, a vapor or a liquid, is conveyed and which are contacted exteriorly thereof by the cooling air. The dry-cooling section may serve to condense vaporous media and, in fact, may be used for the purpose of permitting the heat generarted by a power plant to be conveyed to the atmosphere. In particular, the dry-cooling section may serve the purpose of permitting the heat generated during the condensation of the exhaust gases of a turbine to escape to the atmosphere. The wet-cooling and dry-cooling sections may be arranged within a cooling tower in the form of a multiple arrangement. A ventilator may be provided in order to accelerate and mix the heated, dry air stream and the heated, liquid-enriched air stream emitted from the respective cooling sections.
Although the principle of combining the wet-cooling and the dry-cooling systems has been known for a long time, installations including such a combination have only come into very limited use in practice. The reason for this resides in the great difficulties related to the practical aspect of carrying out and using the method in conjunction with such installations. One of the primary difficulties is associated with the cooling aspect, that is, relates to the cooling medium air, and resides in the fact that the two heated air streams must be thoroughly mixed prior to leaving the installation in order to achieve the desired effect of avoiding the formation of vapor mist. Another difficulty which is associated with severe problems relates to the matter of coupling the cooling system with the source of heat, which latter is usually the waste heat of a power plant. In addition, a combined wet-cooling and dry-cooling system entails a costly structural design which raises grave doubts with respect to the economy of such installations.
In one known type of installation for the cooling of hot water, the wet-cooling and dry-cooling sections are arranged one above the other. Here, the water to be cooled is admitted into a distribution vessel located above the dry-cooling section and first flows through the latter which, in this case, consists of vertical, finned pipes. Thereafter, the water flows through the wet-cooling section which is arranged below the dry-cooling section. The cooling air enters the installation in the form of a cross-current in horizontal direction and the air streams for the wet-cooling and dry-cooling sections are conveyed parallel to one another. The cooling air is conveyed by means of a single ventilator which creates a suction.
In this construction, the problem of mixing the heated air streams may be satisfactorily solved to a degree. However, great problems arise with respect to the heating aspect, that is, relating to the water which is to be cooled. On the one hand, since the wet-cooling and dry-cooling sections are arranged one above the other, a large head of water is created, that is, the water to be cooled must be pumped over a substantial vertical distance, which leads to losses in the economy of the operation. On the other hand, the entire quantity of water to be cooled flows through the wet-cooling section. This leads to significant disadvantages such as, for instance, fouling and oxygen pick-up. Moreover, the dry-cooling section, which consists of finned pipes, must be of a corrosion-resistant construction and, because of the unavoidable fouling which occurs, must be readily accessible for the purpose of observation and cleaning.
Another known construction wherein wet-cooling and dry-cooling systems are combined consists of a cooling tower which is provided with positive-pressure ventilators, that is, ventilators which force the cooling air through the cooling tower. The ventilators convey the cooling air in the form of a wet gas stream, i.e., a stream used for wet-cooling, and a dry gas stream, i.e., a stream used for dry-cooling. The streams are separated from one another by means of walls. In this arrangement, however, the desired thorough mixing of the air streams leaving the various cooling sections is not achieved and, consequently, the formation of a vapor mist is not satisfactorily prevented. Furthermore, the dividing walls lead to additional constructional expenditures.
Finally, there is known still another construction for wet-cooling and dry-cooling wherein the gases for the wet-cooling and the dry-cooling circulate in closed paths arranged within a round cooling tower. The paths are arranged adjacent one another with the paths for the wet-cooling gas alternating with those for the dry-cooling gas and the gases are conveyed along the paths by means of a suction-generating ventilator. A vertical heat exchanger for each of the dry-cooling paths is mounted at the periphery of the cooling tower whereas the spray devices for the wet-cooling paths are arranged horizontally within the confines of the cross section of the cooling tower. This construction is, however, very complicated and, consequently, expensive. Moreover, dividing walls are necessary between the individual streams of gas. In addition, due to the fact that the wet-cooling and dry-cooling sections are disposed one within the other, the distribution system for the water to be cooled is necessarily of great complexity and of high cost.
It is, therefore, apparent that improvements in the state of the art are desirable.